OBJECTIVE: Diagnosing autoimmune encephalitis (AIE) is difficult in patients with less fulminant diseases such as epilepsy. However, recognition is important, as patients require immunotherapy. This study aims to identify antibodies in patients with focal epilepsy of unknown etiology, and to create a score to preselect patients requiring testing. METHODS: In this prospective, multicenter cohort study, adults with focal epilepsy of unknown etiology, without recognized AIE, were included, between December 2014 and December 2017, and followed for 1 year. Serum, and if available cerebrospinal fluid, were analyzed using different laboratory techniques. The ACES score was created using factors favoring an autoimmune etiology of seizures (AES), as determined by multivariate logistic regression. The model was externally validated and evaluated using the Concordance (C) statistic. RESULTS: We included 582 patients, with median epilepsy duration of 8 years (interquartile range = 2-18). Twenty patients (3.4%) had AES, of whom 3 had anti-leucine-rich glioma inactivated 1, 3 had anti-contactin-associated protein-like 2, 1 had anti-N-methyl-D-aspartate receptor, and 13 had anti-glutamic acid decarboxylase 65 (enzyme-linked immunosorbent assay concentrations >10,000IU/ml). Risk factors for AES were temporal magnetic resonance imaging hyperintensities (odds ratio [OR] = 255.3, 95% confidence interval [CI] = 19.6-3332.2, p < 0.0001), autoimmune diseases (OR = 13.31, 95% CI = 3.1-56.6, p = 0.0005), behavioral changes (OR 12.3, 95% CI = 3.2-49.9, p = 0.0003), autonomic symptoms (OR = 13.3, 95% CI = 3.1-56.6, p = 0.0005), cognitive symptoms (OR = 30.6, 95% CI = 2.4-382.7, p = 0.009), and speech problems (OR = 9.6, 95% CI = 2.0-46.7, p = 0.005). The internally validated C statistic was 0.95, and 0.92 in the validation cohort (n = 128). Assigning each factor 1 point, an antibodies contributing to focal epilepsy signs and symptoms (ACES) score ≥ 2 had a sensitivity of 100% to detect AES, and a specificity of 84.9%. INTERPRETATION: Specific signs point toward AES in focal epilepsy of unknown etiology. The ACES score (cutoff ≥ 2) is useful to select patients requiring antibody testing. ANN NEUROL 2021;89:698-710.

August Pi i Sunyer Biomedical Research Institute Barcelona Spain

Department of Immunology Erasmus MC University Medical Center Rotterdam the Netherlands

Department of Neurology 2nd Faculty of Medicine Charles University Motol University Hospital Prague Czech Republic

Department of Neurology Academic Center for Epileptology Epilepsy Center Kempenhaeghe Heeze the Netherlands

Department of Neurology Erasmus MC University Medical Center Rotterdam the Netherlands

Department of Neurology Leiden University Medical Center Leiden the Netherlands

Department of Neurology Maastricht University Medical Center Maastricht the Netherlands

Department of Neurology Stichting Epilepsie Instellingen Nederland Heemstede the Netherlands

Department of Psychiatry and Neuropsychology School for Mental Health and Neuroscience Maastricht University Medical Center Maastricht the Netherlands

Faculty of Health Medicine and Life Sciences School of Health Professions Education Maastricht University Maastricht the Netherlands

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